End stage liver disease and liver cancer are major health concerns for individuals with hepatitis C virus (HCV) infection. Current therapies for HCV aim to halt and reverse the progression of liver injury. These therapies are based on interferon (IFN) and are expected to continue to be based on IFN for the foreseeable future. Both host and viral factors influence treatment outcome. Published data show that viral point mutations in the core gene are associated with treatment failure and insulin resistance. Of great interest, these same mutations (in codons 70 and 91) are associated with the development of liver cancer. These highly specific viral point mutations provide a unique opportunity to investigate HCV-related liver damage and treatment failure at the molecular level. We recently discovered that the disease-associated mutations in codons 70 and 91 have a profound effect on HCV gene expression: They alter the level of two newly identified viral proteins, 70 minicore protein and 91 minicore protein. In a major finding, we discovered that the disease-associated mutation in codon 91 enhances the internal initiation of protein synthesis at codon 91. Our data add to earlier evidence that HCV uses divergent modes of translation initiation to evade cellular antiviral defenses and to increase viral fitness. To account for minicore production, we propose that the core gene contains an extensive and highly conserved translational machine that promotes the internal initiation of protein synthesis at specific sites, driving minicore synthesis and enhancing IFN resistance and viral persistence. The impact of mutations in codons 70 and 91 on the IFN sensitivity of viruses and on the structure and function of minicore proteins will be investigated in Aim I. The properties of the translational machine and the effect of the disease-associated mutations on its activity will be determined in Aim II. Accomplishment of our Aims will fill fundamental gaps in the understanding of the HCV life cycle and provide basic information needed to design interventions to block the action of the translational machine and to inhibit the effects of the minicore proteins in patients.